4.9 KiB
Concepts
EVM Gas Denom
In order to use the EVM and be compatible with existing clients, the gas denom used by the EVM must be in 18 decimals. Since ukava has 6 decimals of precision, it cannot be used as the EVM gas denom directly.
To use the Kava token on the EVM, the evmutil module provides an EvmBankKeeper that is responsible for the conversion of ukava and akava. A user's excess akava balance is stored in the x/evmutil store, while its ukava balance remains in the cosmos-sdk x/bank module.
EvmBankKeeper Overview
The EvmBankKeeper provides access to an account's total akava balance and the ability to transfer, mint, and burn akava. If anything other than the akava denom is requested, the EvmBankKeeper will panic.
This keeper implements the x/evm module's BankKeeper interface to enable the usage of akava denom on the EVM.
x/evm Parameter Requirements
Since the EVM denom akava is required to use the EvmBankKeeper, it is necessary to set the EVMDenom param of the x/evm module to akava.
Balance Calculation of akava
The akava balance of an account is derived from an account's spendable ukava balance times 10^12 (to derive its akava equivalent), plus the account's excess akava balance that can be accessed via the module Keeper.
akava <> ukava Conversion
When an account does not have sufficient akava to cover a transfer or burn, the EvmBankKeeper will try to swap 1 ukava to its equivalent akava amount. It does this by transferring 1 ukava from the sender to the x/evmutil module account, then adding the equivalent akava amount to the sender's balance in the module state.
In reverse, if an account has enough akava balance for one or more ukava, the excess akava balance will be converted to ukava. This is done by removing the excess akava balance in the module store, then transferring the equivalent ukava coins from the x/evmutil module account to the target account.
The swap logic ensures that all akava is backed by the equivalent ukava balance stored in the module account.
ERC20 token <> sdk.Coin Conversion
x/evmutil facilitates moving assets between Kava's EVM and Cosmos co-chains. This must be handled differently depending on which co-chain to which the asset it native. The messages controlling these flows involve two accounts:
- The initiator who sends coins from their co-chain
- The receiver who receives coins on the other co-chain
When converting assets from the EVM to the Cosmos co-chain, the initiator is an 0x EVM address and the receiver is a kava1 Bech32 address.
When converting assets from the Cosmos co-chain to the EVM, the initiator is a kava1 Bech32 address and the receiver is an 0x EVM address.
Cosmos-Native Assets
sdk.Coins native to the Cosmos co-chain can be converted to an ERC-20 representing the coin in the EVM. This works by transferring the coin from the initiator to x/evmutil's module account and then minting an ERC-20 token to the receiver. Converting back, the initiator's ERC-20 representation of the coin is burned and the original Cosmos-native asset is transferred to the receiver.
Cosmos-native asset conversion is done through the use of the MsgConvertCosmosCoinToERC20 & MsgConvertCosmosCoinFromERC20 messages (see Messages).
Only Cosmos co-chain denominations that are in the AllowedCosmosDenoms param (see Params) can be converted via these messages.
AllowedCosmosDenoms can be altered through governance.
The ERC20 contracts are deployed and managed by x/evmutil. The contract is deployed on first convert of the coin. Once deployed, the addresses of the contracts can be queried via the DeployedCosmosCoinContracts query (deployed_cosmos_coin_contracts endpoint).
If a denom is removed from the AllowedCosmosDenoms param, existing ERC20 tokens can be converted back to the underlying sdk.Coin via MsgConvertCosmosCoinFromERC20, but no conversions from sdk.Coin -> ERC via MsgConvertCosmosCoinToERC20 are allowed.
EVM-Native Assets
ERC-20 tokens native to the EVM can be converted into an sdk.Coin in the Cosmos ecosystem. This works by transferring the tokens to x/evmutil's module account and then minting an sdk.Coin to the receiver. Converting back is the inverse: the sdk.Coin of the initiator is burned and the original ERC-20 tokens that were locked into the module account are transferred back to the receiver.
EVM-native asset conversion is done through the use of the MsgConvertERC20ToCoin & MsgConvertCoinToERC20 messages (see Messages).
Only ERC20 contract address that are in the EnabledConversionPairs param (see Params) can be converted via these messages.
EnabledConversionPairs can be altered through governance.
Module Keeper
The module Keeper provides access to an account's excess akava balance and the ability to update the balance.